Preparation of η5-pyranyltricarbonylmanganese complexes and pyrylium triiodide salts from cyclomanganated chalcones and alkynes

Article abstract of DOI:10.1016/0022-328X(95)05741-7

Derivatives of [[1-phenyl-2-phenylcarbonyl-KO]ethenyl-KC¹]tetracarbonylmanganese, i.e. chalcone (1, 3-diphenylprop-2-en-1-one) cyclomanganated at the β-position, undergo insertion reactions with alkynes under reflux in carbon tetrachloride to give [2,4-diphenylpyranyl-η⁵]Mn(CO)₃ derivatives, the reaction being highly regioselective in the case of unsymmetrical alkynes. Reaction of the pyranyl-Mn(CO)₃ complexes with iodine in carbon tetrachloride gives pyrylium triiodide salts in excellent yield. The reaction of one pyranyl complex, [2-(4-chlorophenyl)-6-phenyl-4-(4-trifluoromethylphenyl)pyranyl-η⁵]tricarbonylmanganese (2d), with Na[Fe(CO)₂Cp], gave the demetallated ring-opened isomers E,E-1-phenyl-3-(4-trifluoromethylphenyl)-5-(4-chlorophenyl)penta-2, 4-dien-1-one (10a) and E, E-1-(4-chlorophenyl)-3-(4-trifluoromethylphenyl)-5-phenylpenta-2,4-dien-1-one (10b). X-ray crystal structure determinations of [2-methyl-4,6-diphenylpyranyl-η⁵]tricarbonylmanganese (5) and 2,6-diphenyl-4-(4-trifluoromethylphenyl)pyrylium triiodide (3b) are described, the former being the first reported for a pyranyl-η⁵ metal complex.